1. Field of the Invention
The present invention relates to a process for production of activated carbon fibers from an acrylonitrile based fiber by application of oxidation and activation processings.
2. Description of the Prior Art
Activated carbon is very useful as an adsorbent. Recently, the demand for activating carbon has been increasing particularly in the field of prevention of environmental pollution.
Hitherto, activated carbon has been produced from charcoal, animal charcoal, etc., and it is now possible to produce activated carbon from synthetic resins such as polyvinyl chloride, polyvinylidene chloride, and the like. In addition, a method of producing activated carbon fibers by subjecting the fiber of a phenol resin to carbonization and activation processings is known and described in Applied Polymer Symposium, No. 21, page 143 (1973), for example.
While the use of activated carbon as a fiber has the advantage in that it can be used more functionally than the conventional powdery or granular activated carbon, the above-described method has not been put into practice since the starting materials are quite expensive.
Recently, a method for producing an activated carbon fiber from a polyacrylonitrile fiber has been developed. Japanese patent application (OPI) No. 116332/74 discloses that an activated carbon fiber can be obtained by subjecting a polyacrylonitrile fiber to oxidation in an oxidizing atmosphere at 200.degree.-300.degree. C. without applying tension, and then activating the thus obtained oxidized fiber in an activating atmosphere containing streams and/or CO.sub.2 gas at 700.degree.-1,000.degree. C. without applying tension. Although, by this method an activated carbon fiber having excellent adsorption capacity can be obtained, the mechanical properties of the fiber are very poor. It is difficult to maintain the shape of the activated carbon fiber on handling in actual use.
As a result of extensive investigations directed to overcoming the lack of good mechanical properties it has been found that by adjusting the amount of bonded oxygen in the oxidized fiber to a certain amount on oxidation, and by controlling the shrinkage of the fiber during the oxidation to a limited value an activated carbon fiber having not only an excellent adsorption capacity but also excellent mechanical properties can be obtained.